Aug 5, 2009 (CIDRAP News) – Though infectious disease experts say it is impossible to predict how severe the next wave of the novel H1N1 pandemic will be, experts from the University of Pittsburgh Medical Center (UPMC) observe that it so far resembles the 1957-58 influenza pandemic in several ways. They report that the earlier pandemic caused minimal disruptions, in part because public health officials didn't close schools, cancel public events, or impose travel restrictions.

The group, from UPMC's Center for Biosecurity, published a review of US events during the 1957-58 pandemic in an early online edition of Biosecurity and Bioterrorism: Biodefense Strategy, Practice, and Science. Their findings come a day after Homeland Security Secretary Janet Napolitano said in an editorial board meeting with USA Today that the novel H1N1 pandemic would likely mirror the 1957 pandemic rather than the more severe 1918 episode.

One of the authors of the UPMC report is Dr. D.A. Henderson, who was instrumental in setting up a flu surveillance system at the US Centers for Disease Control and Prevention during the early stages of the 1957 pandemic, according to a UPMC press release. The group's report is based on his experiences, surveillance reports, and contemporary news reports.

"There is need for an understanding in national policy circles of the options for dealing with a pandemic, and time is short if states and local communities are going to be prepared," Henderson said in the press release.

The authors wrote that though no one can predict how a pandemic will unfold, "we would be ill-served if we did not consider past experience." The 1957 pandemic resembles the 2009 pandemic in that both viruses circulated in the summer months in the United States while the virus hit the southern hemisphere during its normal influenza season. Current disease patterns are also similar to the 1957 pandemic: illnesses are generally mild and the virus predominantly strikes younger people. The 2009 pandemic strain also appears to cause a similar case fatality rate to the 1957 strain, they add.

Appearing first at military camps on the East and West Coasts in June 1957, the disease spread quickly. The Association of State and Territorial Health Officers (ASTHO) had a special meeting in August to discuss the threat and response strategies. Epidemiologists weren't sure if the outbreaks would intensify in September or during the normal flu season.

ASTHO recognized that a vaccine could help prevent illnesses and deaths but probably wouldn't be available for at least 2 or 3 months. The group emphasized the role of home care for reducing the burden on hospitals and stated that closing schools and curbing public gatherings would have little impact on preventing the spread of the disease.

Community outbreaks intensified when schools resumed in September, but flu activity started leveling off by the end of November. Schools had 20% to 30% absenteeism rates, but the pandemic had little impact on work absenteeism except in schools and healthcare institutions. The authors estimated that up to 25% of the US population was infected with the virus.

Hospital admissions increased, but facilities had the surge capacity to handle the extra load, the authors reported.

Flu vaccine trials began in July, with efficacy findings ranging from 53% to 60%. From six domestic vaccine producers, 4 million doses were released in August, 9 million in September, and 17 million in October. They produced enough to vaccinate about 17% of the US population. The authors wrote that the vaccine apparently had little effect on the pandemic because of limited availability and efficacy.

One unusual feature of the 1957 pandemic was a 3-month wave of excess flu and pneumonia deaths that began in January 1958, they reported. Surveillance was showing no widespread community outbreaks at the time, and there were no spikes in school closures or work absences. A CDC official at the time speculated that the deaths could have resulted from smaller sporadic outbreaks that didn't attract much public attention.

The 1957-58 pandemic had little or effect on the US and Canadian economies, they found.